Previous methods of customizing or otherwise modifying integrated circuit chips include the use of laser fuse links, one-time electrically programmable anti-fuses and other non-volatile elements such as flash floating gate cells.
Laser fuse links have several inherent disadvantages. These include the high capital cost, the large floor space, and the long manufacturing time required for the tools and processes used to laser blow the links. Also the blowing of a laser fuse must be done prior to final product packaging. This rules out die customization or modification at later steps in the manufacturing process or in the field by the customer. In addition, laser fuses take up significant die area, limiting the number of fuses than can practically be used. This limits the extent to which die customization can be exploited. Also, laser fuses can only be programmed one-time. Later additional or modified customization is not possible.
One-time electrically programmable anti-fuses also suffer from several inherent disadvantages. High voltage and power are required to program the elements. Thus, on-chip high voltage transistors of a sufficiently large size need to be provided. This uses up valuable chip real estate and limits the extent to which die-customization can be exploited. Like laser fuses, these devices can only be programmed one-time. Later additional or modified die customization is not possible.
Flash floating gate cells have yet other inherent disadvantages. High voltage and power are required to program the elements. Thus, on-chip high voltage transistors must also be provided (which as described above takes up chip space). In addition, the process of adding floating gate flash technology to an integrated circuit process is complex and often impractical. Hence, there is a need for a new way to customize integrated circuit chips.